The present invention relates to an optical disc apparatus and an optical disc recording/reproducing apparatus.
Prior art includes, for example, Patent Document 1 (JP-A-2006-14049), Patent Document 2 (JP-A-10-106161) and Patent Document 3 (JP-A-6-290485).
Patent Document 1 describes that “a single recording/reproducing apparatus is required to be provided with a plurality of operation modes having different constraint lengths such as PR(1, 2, 1) and PR(1, 3, 3, 1)”.
Patent Document 1 also describes that “a PR class optimum to each operation mode is able to be selected in this circuit so that the reproducing characteristics are able to be improved”.
Patent Document 2 describes that “a value X given to intersymbol interference for PR equalization is selected in accordance with the characteristics (bit error rates) of waveforms reproduced from the optical disc 1, the characteristics being dependent upon the type of medium of the optical disc 1, and tap coefficients of the transversal filter 3 and discrimination signal levels of the decoder 11 are obtained in accordance with the X value so that even if the type of medium of the optical disc 1 is different, correct reproduction is possible”.
Patent Document 3 describes that “as the control unit 110 is operated to set an optical transmittance of the central portion 112 to “0”, i.e., to a light blocking state, it becomes possible to obtain a ultra high resolution spot having a diameter reduced along the “1” direction similar to the conventional light blocking plate 107 illustrated in FIG. 38. As the control unit 110 is operated to set an optical transmittance of the central portion 112 to “1”, i.e., to a through state, it becomes possible to obtain a usual focusing spot without a ultra high resolution. It is therefore possible to drive a medium having a high recording density with a smaller diameter focusing spot and to drive a medium having a low recording density with a usual focusing spot. It is therefore possible to drive a medium having conventional specifications and a large capacity medium with the same head”.
Patent Document 3 describes that “during recording, a spot diameter is not stopped down. In an amplitude modification of a collimate beam with the modulation unit 111, a laser power loss is large as already pointed out. Because of a limit on a maximum output power of a semiconductor laser of an optical disc apparatus, an upper limit of a data transfer rate (i.e., a disc revolution) is restricted or an upper limit of a recording power usable by a recording medium is suppressed. A loss of a laser power is critical to the performance. It is therefore desired to drive without amplitude modulation during recording and erasing. Driving is possible even if a focusing spot diameter during recording is not stopped down as in the case of reproducing”.
Patent Document 3 describes that “in the eighteenth embodiment, retry reproduction is performed by changing the modulation signal having set so as to obtain a focusing spot judged optimum, in a predetermined range. A possibility of avoiding a disable state of signal reading is therefore increased and reliability of data storage is improved.”